In general, a clutch cover assembly is attached to a flywheel of an engine and is used for transmitting the driving force of the engine towards a transmission. Such a clutch cover assembly mainly includes a clutch cover, a pressure plate and a diaphragm spring. The clutch cover is fixed to the flywheel. The pressure plate is pressed towards the flywheel by the diaphragm spring, and holds a friction member of the clutch disc assembly together with the flywheel while interposing the friction member therebetween. The diaphragm spring has a function of pressing the pressure plate, and also has a lever function of releasing the pressure onto the pressure plate.
When the abrasion of the friction member of the clutch disc assembly herein progresses due to the load characteristic of the diaphragm spring, the pressure load onto the friction member is increased. Therefore, when the friction member is abraded, a large load is required for executing a release operation and a clutch pedal tread force is inevitably increased.
In view of the above, as described in Patent Literature 1, for instance, an abrasion compensating mechanism has been provided that is designed to inhibit increase in pressing load by returning the posture of the diaphragm spring to its initial state even when the friction member is abraded. The abrasion compensating mechanism mainly includes: a fulcrum ring disposed between a pressure plate and a diaphragm spring; an urging mechanism that urges the fulcrum ring in a direction away from the pressure plate; and an abrasion amount detecting mechanism that detects the abrasion amount of the friction member. Here, the diaphragm spring presses the pressure plate through the fulcrum ring. Then, the diaphragm spring is kept at its initially set posture by moving the fulcrum ring to a side away from the pressure plate in accordance with the abrasion amount of the friction member.
On the other hand, an abrasion compensating mechanism described in Patent Literature 2 has been provided for improving instability attributed to vibration in actuating an abrasion amount detecting mechanism. Here, stability in actuation for abrasion compensation is designed by providing a cone spring in the abrasion amount detecting mechanism.